Iron compounds are and can be extremely detrimental to certain organic process streams such as phenolic process streams utilized in the manufacture of bisphenol-A (BPA), which has very low tolerances for iron when the product is to be used for making polycarbonates.
Detrimental levels of iron may find their way into such process streams in processes which employ acid and in which are present ferrous metal parts, pipes, vessels or the like. In spite of strenuous and careful efforts to prevent corrosion, iron contaminants may enter the process far upstream from the final product and still present problems of meeting specifications for the final product.
Specifically with respect to the treatment of bisphenol-A to purify it, the reader may be interested in U.S. Pat. No. 4,107,218, which describes a process of removing color bodies from bisphenol-A wherein the bisphenol-A is passed through a bed of cation exchange resin (a resin which exchanges cations) such as a conventional styrene-divinyl benzene resin wherein a certain portion of the styrene is sulfonated to place strongly anionic sites on the resin. There is much discussion in the patent's specification about the regeneration of the resin in a phenol/water mixture, which then for economic reasons has to be reclaimed by distillation.
Also of interest is East German Pat. No. 134,427, which suggests the use of acid ion exchange resin for the purification of phenol; specifically, various organic impurities are removed by passing the phenol through a bed of acidic ion exchange resin (that is, one containing fixed acid sites capable of exchanging cations).
U.K. Pat. No. 1,539,186 suggests the use of sulfonated styrene/divinylbenzene ion exchange resins which have been partly neutralized with aminothiol-carboxylic acids or esters as catalysts for the manufacture of bisphenol-A from acetone and phenol in a water-dry system.
German Offenlegungschrift No. 2,048,661 discloses the use of fixed beds of strongly acidic and weakly basic ion exchange resins to purify raw bisphenol-A; however, the chemical structure of the resin is not given, nor is a description of the impurities removed. The specification states: "The mechanism of the purification step in the exchange column is not known. It is surmised that in the purification step such components are removed as affect the decomposition of the raw bisphenol-A during distillation, such as acids, alkalies, salts, traces of heavy metals, etc." After treatment with the resin, the product is subjected to a vacuum distillation step to separate the phenol from the bisphenol-A. No description of regeneration is given.
None of the above references addresses the problem of the elimination of iron compounds from the bisphenol-A (BPA) product which are obtained when the BPA is made using a hydrochloric acid catalyst for the reaction of phenol and acetone in contact with even a small surface containing ferrous metal. Also, it is known that conventional ion exchange resins such as the sulfonic acid (strong acid) or carboxylic acid (weak acid) types can be used to remove iron from phenol systems containing more than about 5% water but they will not remove ferric chloride from almost anhydrous phenolic streams. Apparently these conventional ion exchange resins depend upon ionization of the iron salts for their removal but insufficient ionization takes place in phenolic systems containing less than 5% water.